1. Field of the Invention
This invention relates to hub caps for wheel hubs having tapered roller bearing races within a sealed cavity and, more particularly, to hub caps having an air valve through which the sealed cavity can be pressurized to prevent the inflow of water when the wheel hub is submerged in water, as when hubs on a boat trailer are submerged in the water during launching and recovery of the boat.
2. Description of the Prior Art
Referring now to FIG. 1, a conventional boat trailer wheel hub 100 typically has inner and outer tapered roller bearing assemblies 101A and 101B, respectively. Each bearing assembly has an inner race 102 that is mounted on the axle 103, an outer race 104 that is pressed into the hub body 105, and a plurality of tapered rollers 106 mounted in an annular roller retainer 107, which ride against both the inner and outer races. As the races and tapered rollers are fabricated from hardened steel, they are extremely vulnerable to corrosion. Wheel hubs typically have a cavity 108, which is spanned by the axle shaft between the inner and outer bearing assemblies, and open at both ends. The cavity is filled with a high-temperature grease (not shown) in sufficient quantity that the bearing races and rollers are continually bathed in liquified grease as centrifugal force throws the grease against the cavity walls. The grease is retained within the cavity 108 by a hub cap 109, that is pressed into the nose 110 of the hub body 105 and seals the outer opening, and by a flexible, neoprene rubber seal 111, that seals the inner opening. The neoprene rubber seal 111 is molded into a metal retainer ring 112 that is pressed into the inner opening of the hub. A flexible annular lip (not shown) on the neoprene rubber seal 111 rides against a cylindrical sealing surface on the axle shaft.
Though entirely adequate to protect the bearing assemblies from rain, the neoprene seal is unable to provide hermetic sealing when the hub assembly is submerged. Boat trailer wheel hubs are usually submerged in water during each launching and each recovery of the carried boat. Entry of water into the hub cavity occurs via the following mechanism. When the trailer is being towed, friction caused by a combination of continuing movement of the bearing assemblies, contact of the tires with the road and—if the trailer is so equipped—braking generates heat, which causes the air and grease inside the hub cavity to expand. When the hot hub is submerged in water during launching of the boat, the hub cools and the air and grease inside the hub cavity contract, thereby reducing the pressure within the hub cavity below ambient atmospheric pressure. The neoprene rubber seal, which seals most effectively when the pressure within the hub cavity is greater than ambient atmospheric pressure, actually functions as a one-way valve when the pressure gradient is reversed. Water, sand, and other contaminants flow into the hub cavity until the pressure within the hub is equal to the ambient atmospheric pressure. Once water has found its way into the hub cavity, destruction of the bearing assemblies and possibly the axle shaft via corrosion is inevitable.
The problem of bearing corrosion in boat trailer hubs has spawned a multitude of inventions aimed preventing water from entering into the hub cavitys of trailer wheels. Some of the preventative measures covered by these inventions are costly to implement, others are complex, others are costly, and some are ineffective. The following patents are exemplary of the prior art.
In U.S. Pat. No. 3,785,706, issued to Vangalis on Jan. 15, 1974, there is disclosed a pressurized hub cap for a vehicle wheel. The Vangalis patent describes a cup-shaped cap having a flange which seats on the wheel hub. A helical spring urges a piston in the direction of the axle of the trailer to hold grease on the outside of the axle and associated nut. A vent hole is provided on the outside of the piston, and a second hole is provided to allow the escape of grease in the event that excessive expansion of the grease occurs. A similar construction is described in U.S. Pat. No. 4,106,816, issued to August on Aug. 15, 1978. In U.S. Pat. No. 3,955,852, issued to De Puydt et al. on May 11, 1976, there is also described a trailer hubcap device utilizing a spring-biased piston to pressurize grease against the outside of the axle and nut. The De Puydt et al. patent further describes a manual actuator to permit the pressure to be relieved while the trailer is being moved along a roadway.
A related hubcap construction is described in U.S. Pat. No. 3,649,080, issued to Molinare on Mar. 14, 1972. This patent describes a hubcab construction which includes a grease fitting to permit introduction of grease into the cap and also a pressure relief valve to provide for expansion of the grease. In U.S. Pat. No. 3,393,015, issued to Kaufman of Jul. 16, 1968, there is described a hubcap which includes an O-ring normally positioned over a vent hole to prevent the entrance of water within the cap, but which will expand to uncover the hole for permitting air and grease to be vented from the hubcap when heated. A protective hubcap closure is described in U.S. Pat. No. 3,149,883, issued to Reilly on Sep. 22, 1964. The Reilly patent describes a hubcap which is flexible to become contracted or compressed when the trailer is immersed in cold water.
A different approach to the waterproofing for a hubcap is described in the Eberle patent, U.S. Pat. No. 3,226,162, issued on Dec. 28, 1965. The Eberle patent describes the use of a tube connecting from the pressurized tire to the hubcap, for permitting air to be vented into the hubcap as a method for pressurizing the cap to prevent entrance of water.
Several types of pressure relief hub caps have been produced in the past. One type is shown in U.S. Pat. No. 3,785,706 to Van Galis. In this device, a cup shaped seal is mounted within a cup shaped hub cap, with a spring acting on the seal to compress the grease within the hub. A first opening in the cap adjacent the outer end provides for pressure relief in the spring area between the seal and the outer end of the hub cap. A second opening in the hub cap inboard from the first opening provides for escape of grease when the pressure within the hub is sufficient to compress the spring.
Another type of hub cap is shown in U.S. Pat. No. 3,077,948 to Law. This structure utilizes a cup shaped seal sliding in a sleeve with a spring urging the seal inward to compress the grease. The sealing action occurs between the cup shaped seal and an O-ring in the inner surface of the sleeve. A grease fitting is carried in the sliding seal for introducing grease into the hub.
The hub cap of the U.S. Pat. No. 3,785,706 patent suffers from the disadvantage that grease can be added to the hub only by removing the hub cap. This problem is solved by the hub cap of the U.S. Pat. No. 3,077,948 patent. However there are still some disadvantages with this structure. When the hub is being filled with grease by a grease gun, the manual force utilized in holding the grease gun in place also acts to hold the sliding seal in fixed position so that excess pressure can be built up within the hub and the inner bearing seal can be damaged without the operator knowing of this fact. That is, the automatic pressure release operation is nullified by the force applied with the grease gun. Also, the cup shaped seal which slides within the outer sleeve or housing and engages the O-ring for making a seal provides only limited area for escape of grease.
One of the more popular devices for affording protection to the bearings of trailer wheels is covered by U.S. Pat. No. 4,106,816 to August. Known as the “Bearing Buddy”, the device is a specially designed hub cap having a sliding piston with a centrally-positioned grease fitting. The piston is biased with a coil spring and is designed to maintain the bearing bathed in grease. One of the problems with this device is that it is impossible to remove all of the air from the cavity by injecting grease from the outer end of the hub, as the inward hub seal will prevent the escape of pressurized air that builds up as grease is injected into the bearing cavity. Because the trapped air and grease have different rates of expansion, it is difficult for the device to work as intended. Another problem is that the spring constantly pressurizes the bearing cavity of the wheel hub. This added pressure forces the wiping portion of the inner neoprene seal more firmly against the outer surface of the axle shaft. The added pressure increases the wear rate of the seal.
Accordingly, it is an object of the present invention to provide a new and improved hub cap that is both simple to use and inexpensive to manufacture, for sealing against the entrance of moisture into the bearing cavity. It is the intent of the present invention to prevent water and other contaminants from entering a boat trailer wheel hub by providing temporary pressurization of the wheel hub cavity at times when the boat trailer must be partially submerged during the launch and recovery of a boat.